Investigations will be undertaken to define the molecular defect in the neurovisceral storage disease fucosidosis. Immunochemical studies (double immunodiffusion, precipitation and inhibition reactions, and radioimmuno-competitive binding assays) will be undertaken using the IgG fraction of anti-alpha-L-fucosidase antibody to determine whether fucosidosis patients biosynthesize an antigenically similar, but structurally altered, alpha-L-fucosidase. If present, the mutant alpha-L-fucosidase will be purified from tissues (liver, fibroblasts) from patients with fucosidosis by affinity chromatography, kinetically characterized and compared to the properties of the normal enzyme.